Is it possible to set the same keyframes values for another property?
So I found a pretty good way, using bpy. I post it if someone needs

import bpy
from bpy import context



for obj in bpy.context.selected_objects:
    print(obj.name)
    bpy.context.view_layer.objects.active = obj
    obj = bpy.context.active_object
    for fc in obj.data.animation_data.action.fcurves:
        if fc.data_path == "bevel_factor_end":
            list_co = list()
            my_fc = fc
        for pt in my_fc.keyframe_points:
            print(pt.co.x, pt.co.y)
            list_co.append(pt)
my_fc = obj.data.animation_data.action.fcurves.new("bevel_factor_start", index=-1)
for pt in list_co:
    my_fc.keyframe_points.insert(pt.co.x, pt.co.y)
for fc in obj.data.animation_data.action.fcurves:
    if fc.data_path == "bevel_factor_end":
        obj.data.animation_data.action.fcurves.remove(fc)